In recent years, research on various organic electronic devices such as organic electroluminescent (hereinafter, may also be referred to as “organic EL”) displays, organic EL lightings, organic semiconductors and organic solar cells has been actively conducted, and these devices are expected to serve as the next-generation displays that will replace liquid crystal displays (LCD's), or as the next-generation lightings that will replace light emitting diode (LED) lightings. Furthermore, since organic EL elements are such that all of the constituent elements thereof can be formed from solid materials, there is a possibility that organic EL elements may be used as flexible displays or lightings. An organic EL element has a basic configuration in which an anode layer, a light emitting layer, and a cathode layer are sequentially formed on a substrate made of glass or the like. As an electric current is passed between the anode layer and the cathode layer, the organic EL element becomes self-luminous, and light can be extracted from either side of the anode layer and the cathode layer. Therefore, a top emission mode and a bottom emission mode are available as the light emission mode of organic EL devices.
However, regarding the organic EL elements described above, if moisture, impurities and the like exist in the periphery of an element, oxidation of an electrode, oxidation decomposition of an organic material caused by heat generated when the element is driven, degeneration of an organic material, or the like occurs, and thus non-light emitting areas called dark spots are generated. When the dark spots grow to have a diameter of several ten micrometers (μm), the non-light emitting areas can be identified by visual inspection, and this leads to deterioration of visibility.
As a means for suppressing such a problem, a technique has been examined in which an organic EL element is sealed so that contact with moisture or oxygen is suppressed. For example, a technique is disclosed in which a sealing can is pasted by using a sealing material to a substrate having an organic EL element formed thereon, and a desiccant is attached to the inside of the sealing can so as to seal and dry the organic EL element, thereby preventing moisture from infiltrating to the organic EL element (for example, see Patent Document 1). However, in the method of using such a glass sealing can, there are problems in that the glass sealing can is fragile to impact and easily broken during the dropping test, and in that glass with a cavity is expensive.
In this regard, a method is considered in which an element substrate of an organic EL element and a sealing substrate such as a glass plate are pasted to each other with a sealing material interposed therebetween so as to seal the organic EL element. A sealing material using a light curable resin (for example, see Patent Document 2) and a sealing material containing an epoxy resin and an acid anhydride as main components (for example, see Patent Document 3) are disclosed. Further, a transparent sealing material which does not contain a curable resin and contains a diene polymer and a liquid softening agent as main components and which is excellent in flexibility is disclosed (for example, see Patent Document 4).